The present invention relates to an electrical socket, and particularly to an electrical socket supporting an integrated circuit (IC) chip and being securely surface mounted to a circuit board thereby achieving reliable interconnection between the IC chip and the circuit board.
An integrated circuit chip is commonly mounted to an electrical socket which then is secured to a circuit board via soldered connections between contacts of the socket and the circuit board. At present, the soldering connections between a socket and a circuit board are usually achieved by surface mount technology (SMT) or through hole technology (THT). THT has become less frequently employed since the required through holes do not make an efficient use of space on a circuit board. SMT is used in a wide range of applications due to the small space requirement on a circuit board.
A conventional socket is disclosed in U.S. Pat. No. 5,746,608. Contacts of the socket are adapted to provide electrical connection between the socket and a circuit board.
Another conventional socket is shown in FIG. 3. An electrical socket assembly 8 comprises a dielectric base 80, a plurality of contacts 81, a circuit board 82 and a chip module 83. The base 80 defines a plurality of engaging slots 84 communicating with the receiving chambers 85. The contacts 81 are received in corresponding receiving chambers 85. One end 88 of each contact extends outside of the receiving chambers for being surface mounted to the circuit board 82 via a solder ball 86 attached thereto. The chip module 83 comprise a plurality of engaging terminals 87 extending into the receiving chambers 85 through the engaging slots 84 to electrically engage with the corresponding contacts 81. Electrical communication between the chip module 83 and the circuit board 82 is thereby achieved.
However, differences in coefficients of thermal expansion (CTE) between a socket and a corresponding circuit board cause problems in conventional surface mount connections. Misalignment between contacts of the socket and corresponding soldering pads of a mating circuit board caused by the CTE problem results in poor communication quality. Furthermore, in the second example discussed above, the solder balls 86 easily wick into the receiving chambers 85 when melted during the surface mount procedure thereby adversely affecting the quality of the connection. Therefore, an improved socket is required for eliminating the negative effects resulting from the CTE problem and for preventing solder from wicking into an interior of the socket.